Although a wrecked spaceship and an exploded home planet will keep Alf--the furry, big-nosed alien with his own NBC sitcom--grounded here on Earth for the rest of his prime-time days, Christmas sales of products bearing his likeness are soaring out of this world. The show's producers are getting rich quicker than their mischievous space traveler can spout his Borscht Belt one-liners.

Alf, the poster, is reportedly outselling not only the rock group Bon Jovi but even Vanna White decked out in her "Wheel of Fortune" finest.

Retail sales for all Alf products will exceed $250 million this year in this country alone, says Sid Kaufman, vice president of Leisure Concepts, the division of Lorimar Telepictures charged with selling licenses for Alf products. And with "Alf" now airing in more than 50 countries, Kaufman expects international sales to surpass $20 million.

"Alf is not like a typical Saturday morning cartoon character," Kaufman says, even though Alf has starred in his own Saturday morning cartoon since September as well. "Exposure to such a large audience on NBC each week is such a tremendous advantage, I doubt we could do this without it."

While characters from prime-time series often make the jump to merchandising--"The A-Team," "The Incredible Hulk," "The Dukes of Hazzard," even J. R. Ewing from "Dallas"--Kaufman and his licensees insist that few have ever appealed to as broad an audience, as "Alf" zoomed into the Nielsen Top 15 this year.

"It's a fabulous character for us," says Barbara Wruck, vice president of Coleco, the toy maker that manufactures three different Alf dolls which, she says, will ring up $85 million in sales this year. "It has tremendous appeal to both children and adults. I know many an adult who asked for an Alf doll for Christmas."

Coleco was so certain that Alf would catch on that it jumped at the chance to produce a line of Alf dolls two months before the space traveler from Melmac ever crash-landed on America's television screens in the fall of 1986.

Although many critics said the show would flop--some predicted "Alf" wouldn't last for more than four episodes--Coleco offered Leisure Concepts and the show's producers a large advance and a percentage of the wholesale revenues.

As a talking, walking Alf hit the air last year, Coleco rushed a stuffed Alf to toy stores in time for Christmas. It sold out everywhere. Though "Alf" enjoyed only moderate ratings success in its first season, the scramble to grab an Alf license was on.

Neither Kaufman nor Bernie Brillstein, the show's executive producer, would say how much money they are making from Alf merchandising. Brillstein did say that Disney, 20th Century Fox and Universal all offered him "something in the high seven figures" for ownership rights to Alf, and he is glad that he rejected them all.

"Alf is a merchandising dream," says Paul Fusco, Alf's creator and producer of the television show. "Not even the Muppets had their own weekly prime-time show. But that's not the important thing. We are not in the toy business."

Fusco says that Alf was created exclusively to star in a television series and that the potential merchandising success was never a consideration in the development of the character or the show. Even with Alf's face already plastered on nearly everything under the planet Melmac, Fusco says he will not let Alf sell out.

"We're trying to keep a quality check on what we put his name on," Fusco says. "I don't want it to look like we're doing everything. It has to be an important, useful or a fun product."

Fusco and Tom Patchett, the co-creator and executive producer of "Alf," say that Alf's fans have become so passionately attached to him that the producers feel a tremendous responsibility to do good by that audience.

While they do charge $6 for membership to the Alf Fan Club--more than 8,000 people have joined so far--Fusco and Patchett also encourage Alf to spend a good deal of his time, free of charge, helping the Make a Wish Foundation fulfill the dreams of terminally ill children.

Meantime, the men behind Alf continue to propel him toward the financial stratosphere. "Alf: The Movie" will be shot next spring, and Leisure Concepts is looking to expand its merchandising opportunities overseas. In an effort to keep the Alf product line fresh, they have also begun to hawk licenses for Alf's Saturday morning cartoon friends.

Those involved with merchandising Alf worry that with so many Alf products, Alf-mania will burn itself out soon. But, if they keep the quality up, Brillstein believes that, as Mickey Mouse and Kermit the Frog before him, Alf will live long and prosper.

"We believe Alf can become a part of America," Brillstein says, "and not just the latest TV phenomenon."